Clinical Features of Lewy Body Dementia
Lewy body dementia presents with four core clinical features: fluctuating cognition with pronounced variations in attention and alertness, recurrent well-formed visual hallucinations, spontaneous parkinsonism (bradykinesia, rigidity, tremor, postural instability), and REM sleep behavior disorder where patients act out their dreams. 1, 2
Core Diagnostic Features
Fluctuating Cognition
- Cognitive changes manifest as impairments in attention or somnolence with variations in alertness occurring over minutes, hours, or days 1
- These fluctuations can be assessed using validated scales including the Mayo Fluctuations Scale, Clinician Assessment of Fluctuation (CAF), or Dementia Cognitive Fluctuation Scale 1, 3
- Patients may experience transient episodes of unresponsiveness related to fluctuations in attention and consciousness 2
Visual Hallucinations
- Recurrent visual hallucinations are typically well-formed and detailed, often involving people, animals, or objects 1, 2
- These hallucinations are a distinguishing feature from Alzheimer's disease, where visual hallucinations are not a core feature 2
- Patient and caregiver education about the nature of hallucinations can significantly reduce anxiety, and simple coping strategies like eye movements, changing lighting, or distraction techniques can be effective 1
Parkinsonism
- Spontaneous extrapyramidal motor symptoms include bradykinesia, rigidity, tremor, and postural instability 1, 2
- These motor features occur without prior exposure to neuroleptic medications 2
- The presence of prominent parkinsonism combined with visual hallucinations strongly suggests Lewy body dementia rather than Alzheimer's disease 2
REM Sleep Behavior Disorder (RBD)
- Patients act out dreams during sleep due to lack of normal muscle paralysis during REM sleep 1, 2
- RBD may precede cognitive symptoms by years, making it a valuable early diagnostic marker 2
- Polysomnography can confirm this diagnosis and serves as an indicative biomarker 4
Supportive Clinical Features
Autonomic Dysfunction
- Orthostatic hypotension, urinary incontinence, and constipation are common manifestations 2, 3
- These autonomic features occur in both dementia with Lewy bodies and Parkinson's disease dementia 3
Cognitive Profile
- Characteristic impairments involve attention, executive function, and visuospatial abilities rather than primary memory deficits 1, 2
- The Montreal Cognitive Assessment (MoCA) is more valid than the MMSE because it includes items assessing attention and executive functions like working memory 1
- The MMSE has limited sensitivity for detecting executive dysfunction and has floor effects in severe dementia 1
Pathophysiological Features
Protein Deposition Pattern
- Abnormal accumulation of α-synuclein within inclusions called Lewy bodies, as well as α-synuclein-immunoreactive neurites and diffuse cytoplasmic immunoreactivity 1
- Disease progression typically begins in the medulla oblongata, pontine tegmentum, and olfactory system, followed by involvement of the substantia nigra and other deep gray nuclei, and finally deposition in the cortex 1, 2
- Neocortical Lewy body disease is considered adequate explanation for cognitive impairment or dementia 1
Coexisting Pathology
- Lewy body dementia frequently coexists with Alzheimer's disease pathology, particularly in older individuals 1
- Amyloid-positive biomarkers do not exclude Lewy body dementia diagnosis when core clinical features are present 2
Critical Clinical Pitfalls
Neuroleptic Sensitivity
- Traditional antipsychotics must be absolutely avoided due to severe neuroleptic sensitivity that significantly increases morbidity and mortality 2, 5
- Atypical antipsychotics should be used cautiously and only when absolutely necessary 6
- Structured activities, calming measures, and support for family and caregivers should be implemented before considering pharmacological interventions for psychotic symptoms 1
Medication Considerations
- Levodopa should be used cautiously for motor symptoms, as dopaminergic agents carry risk of inducing or worsening psychotic symptoms 2
- Cholinesterase inhibitors (donepezil, rivastigmine, galantamine) are first-line treatment for both cognitive symptoms and visual hallucinations 1, 2
- Memantine may be considered as an alternative or adjunctive treatment for cognitive symptoms 1
Diagnostic Biomarkers
Imaging Findings
- DAT scan demonstrates reduced striatal dopamine transporter uptake, providing Level A evidence supporting diagnosis 2, 4
- FDG-PET/CT demonstrates occipital hypometabolism and the "cingulate island sign" 3
- MRI shows relative preservation of medial temporal lobe structures compared to Alzheimer's disease 2, 3
- Brain SPECT shows greater degree of occipital hypoperfusion compared with Alzheimer's disease 5